Former Defense Secretary Leon Panetta issued some words of caution for the United States, advising that North Korea’s bullish attitude was something to watch, not dismiss.

His exact words, as quoted by CNBC: The United States. should be “very concerned” at the level of “provocation and bellicosity” coming from North Korea’s Kim Jong-un, as he leads his country into restarting its nuclear facilities. The United States, South Korea and Japan need to be “very firm in sending them a message that we are going to do everything necessary to defend our security and defend our troops,” and to pay attention to the risks of a North Korean “miscalculation,” he was quoted in CNBC.

Mr. Panetta’s warning comes as the Navy has shifted its guided-missile destroyer, the USS McCain, into waters off the Korean peninsula, and as North Korea has vowed to rebuild and restart its nuclear facilities — including one that is capable of producing a bomb’s worth of plutonium in one year’s time.